I have Slackware64-14.2 with dnsmasq-2.78-x86_64-1_slack14.2 and the following setup:

- 2 Ethernet interfaces: one looks to the real world (EXTERNAL), the other is plugged into a switch (INTERNAL), ip forwarding, NAT
- I run dnsmasq on INTERNAL to provide a DHCP service for the local network
- there's a second desktop that is always plugged into the switch and always gets the same IP address from dnsmasq. I did this with a

line in /etc/dnsmasq.conf

- I also often need to plug different laptops (which I do not own) into the switch and get them connected to the local network after dnsmasq assigns them an IP

Now my goal is to have dnsmasq always assign those different laptops the same IP, just so I could skip the step of looking what IP they got and could immediately ssh into them. How can I do this?

I've been reading the examples in dnsmasq.conf as well as the man page but with no success. Basically I need to tell dnsmasq "assign this fixed IP to any computer which has a network card with a MAC address that is NOT xx:xx:xx:xx:xx:xx". But I did not find anything like:

Is this possible to do?

The way I handle this (for my 192.168.4 address space) is to have the fixed hosts assigned addresses from 192.158.4.2 to 192.168.4.39. Then I have a 'dhcp-range=192.168.4.40,192.168.4.62,12h', so that additional hosts will get an address in that range. If you are always only adding one additional laptop, it will get the 192.168.4.40 address.

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If you are using dnsmasq for local DNS the hostname should automatically resolve to the correct IP address. Just ssh using hostname.

When the laptops are connected you can find their MACS but assigning if not would mean multiple computers could have the same IP address.

Interesting, can I have a 'dhcp-range=192.168.4.40,192.168.4.40'? Yes, it's always just one laptop (but not always the same), but doesn't having an IP range imply that IP addresses get assigned randomly?

I'm not using DNS at all.

I know, I can also find the IP they get from dnsmasq by physically logging into them, but that's exactly the step I'm trying to skip.

Not the behaviour I have observed using dnsmasq.

Hi,
I'm not using dnsmasq, but generally it should be allowd to have an DHCP-Scope with only one address. If it doesn't just allow 2 IPs in that range and give the other one to "2nd desktop" you've mentioned in your first post.
But the problem is if the laptop doesn't release the Adress, ie. if it crashes.
Then the DHCP-scope is full and a newly connected laptop won't get any IP since it's still assigned to another MAC address. Before reducing DHCP Lease Time be aware, that clients may ask the server for keeping the leased address when 50% of the lease duration is expired.

But why even bother? Just take a look into the arp table of the computer you're using for ssh-client. As long as its in the same logical network (192.168.4.x probably), the "arp" command will list the local devices.

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